How do you pass shielded servo motor cables through the cabinet wall/panel?

andypugh wrote:

You mention "shielded" so my favoured Neutrik (SpeakCON and PowerCON) won't work.

Yeah, it seems shielded motor cables (as well as IO cables) is the standard? Even my old Yaskawa SGDA manual (from the 1990's) shows shielded motor cables (both power and encoder).

For the shield to be effective against EMI it's apparently important to clamp the shield to ground through a very low impedance path, which means stripping a bit of the outer insulation and strapping the shield to a ground plate or similar, with a strap that encircles the cable. A pigtail at the end of the cable isn't very effective, apparently.

This strapping takes a lot of space and is generally impractical, so why not do the connection where the cable passes the enclosure wall? That's my thought, anyway.

andypugh wrote:

I used M23 to pass the power and feedback for the 4th axis through the mill to allow it to be disconnected.

I looked through the catalog and it seems these are meant to be used on the motors exclusively - there are no versions of the mains voltage rated connectors with female receptacles? AND they require a €1000 (€969.19 to be exact ) tool for proper crimping...

I haven't tracked down a Lemo catalog, but I assume these have the same problem with either solder or buy a very expensive crimper?

andypugh wrote:

And, that mention of D-sub brings me to the real point of this reply. Ordinary D-sub have a higher current and voltage rating than you might guess:
docs.rs-online.com/869a/A700000007669880.pdf
750V and 5A, and it's not a fancy one.

The contacts may have ok voltage and current ratings, but the wimpy solder cups surely aren't suitable for mains voltage? Also, max 0.5 mm² cables.

The fancy ones might actually be workable though, accepting soldering?! At least the "high power" pins (FMP005P103 + FMP005S103) have beefy solder cups. And the cost seems okay too! (The pins don't have an explicit voltage rating but the "Connector Electrical Data" for the contact bodies says "Test voltage between 2 contacts or shell and contact: 1000 V".) But I'm not clear on how to properly connect the shield braid to a panel mounted socket. A backshell won't fit there?

Anyway, it's interesting to see how people handle this given the limited options available.

I found this video from Siemens that shows how to connect motor power cable shields:

After looking into this some more, the takeaways seem to be:

* Connect shield using circular, 360° connection. No pigtails (these have too high impedance at higher frequencies).
* Shield must be connected at both ends. Specifically, the shield should be connected to the motor frame and to the drive "chassis". This is because the shield is the return path of common mode noise from the drive, and if it's only connected at one end obviously this won't work. (I guess a ground conductor in the cable could serve this purpose as well except it might have too high impedance at high frequencies due to the skin effect?)
* If shield is connected to the cabinet mounting plate next to the drive, the plate must be unpainted under the drive. (Unpainted and well grounded mounting plate seems to be strongly recommended in general, perhaps for other reasons too?)
* An EMI cable gland can optionally be used at the entrance to the cabinet, but this is not a substitute for a proper connection of the shield at the drive. I'm not clear on the benefits of this, if any.

Sources: the Siemens video above, Danfoss Facts worth knowing about AC Drives , Electrical Engineering Portal .

The qc connectors are rated at 20 amps. There is a much larger one but it did not fit my crimper. For the shield, I pass it through into the cabinet using a 5 pin connector and then terminate at the drive GND connector.. I also split the shield into two at the drive. One half goes to the drive and I fold back the other half to a QC spade covered by shrinkwrap. I then run an unshielded wire from a copper terminal on the enclosure to the spade. So the drive is attached to the cable shield and the enclosure frame ground.

You might also like to look at a motion cable specialist like this Aussie one.
treotham.com.au/product-categories
I source my flexible cable from these guys and they have some industrial ethernet connectors and ethernet cable that are rated for cable chains and industrial connectors which would be good for distributed ethercat etc.

Regarding grounding of shields:

I have often seen the recommendation for NOT using twisted shield as a pigtail. And that a round clip to ground plane must be used.

But I struggle to find sources for ground clamps. I have tried many different terms. Tried elemwnt14, rsonline, AliExpress.

Options seem to be limited.

Anyone know of a good source?

I just ordered some of these . TME have different sizes too, search for KTCC-5 and KTCC-9 for example. I agree they are surprisingly difficult to find. They're apparently called P-Clips.

Another type, T-clips, fastens with two screws and span the cable (so should give excellent strain relief as well), but I couldn't find reasonably priced ones made of metal.

I use one of these variants
 

So if you use a ground clamp as suggested by above links above, how do you connect the shield to the drive connector terminal block?